| 摘要 |
A high impedance transducer 102, for example a capacitive transducer or a MEMS microphone, is biased using a voltage generator such as a charge pump 100 whose output voltage 202 has a stable relationship with its input voltage 306, that is itself controlled based on a calibration value, that can be supplied by an adjustable potential divider 305. The calibration value can be set by applying a test signal of known amplitude and monitoring the response, to produce a transducer output signal of predetermined amplitude. An input voltage control circuit 300 need not be connected to the bias output and can comprise a voltage reference Vref, an amplifier 302 a feedback circuit 305 and an adjustable potential divider 305 including an array of resistors and switches, the calibration value possibly stored in a memory. The biasing circuit can be used in ultrasonic imagers, a sonar transmitter/receiver, a communication device or a personal audio device such as an MP3 player and achieves stable biasing without loading of the bias output by a feedback loop. |
